Fluid fuel injector for an internal combustion engine

ABSTRACT

An injector in a spark ignition engine combustion chamber has an injector body containing a needle with a closure element co-operating with a fuel passage seat extended by a diffusion port. The needle is axially movable between a first position wherein the closure element bears against the seat and a second position wherein the closure element is away from the seat, It further has a single-piece diabolo-shaped element fixed in the downstream part of the body, The seat, the diffusion port and a bore for slidingly guiding the needle are formed in the one-piece element. It defines, with the body downstream part of the body a fuel supply chamber and has ports communicating the chamber with the bore immediately upstream of the seat and emerging tangentially in the bore.

BACKGROUND OF THE INVENTION

The present invention relates to injectors for injecting fuel in thefluid state, and in particular in the liquid state, and designed toinject the fuel directly into a combustion chamber of a controlledignition engine. It is particularly applicable to injecting gasoline,but it can also be adapted to other liquid fuels, such as alcohol-basedfuels, and liquefied petroleum gas.

Direct injection injectors are already known comprising an injector bodycontaining a needle that is axially movable by electrical control means(often constituted by a coil) and terminated by a shutter element, oftenof hemispherical shape, that co-operates with a seat for passing fuel.The needle is movable between a first axial position in which theshutter element bears against the seat, and a position in which it isspaced apart therefrom.

The stresses imposed on the injector for direct injection are muchgreater than those imposed for indirect injection into the manifold. Itis necessary simultaneously to limit the penetration depth of the fueljet, e.g. to avoid wetting the walls of the chamber, and to providemixing between air and fuel that is as intimate as possible for bettercombustion, and to do this even though the time available for injectingfuel is very short.

To achieve this result, attempts have already been made to impartturbulent motion to the fuel.

Patent application FR 98/00554 describes an injector having a chamberfor putting the fuel into rotation about the axis of the shutterelement, which chamber is situated upstream from the seat and is definedbetween a plurality of elements.

SUMMARY OF THE INVENTION

The present invention seeks in particular to provide a fuel injectorthat satisfies practical requirements better than previously knowninjectors, in particular in that it causes the fuel to be set intorotation by using means that are simple to implement, but neverthelesshighly effective. The invention seeks in particular to reduce the “dead”volume that the injected fuel occupies without being set into rotationwhen the needle begins to open.

To this end, the invention provides an injector comprising a one-pieceelement fixed in the downstream portion of the body, in which elementthere are formed the seat, the spray orifice, and a hole for slidablyguiding the needle, said element being dualcone-shaped or diabolo shapedso as to co-operate with said downstream portion of the body to define afuel feed chamber having bores putting the chamber into communicationwith said hole immediately upstream from the seat and opening outtangentially into the hole, and passages for feeding the chamber.

The dead space is thus restricted to the small volume annular zonesituated between the cylindrical portion of the needle and the circularbearing line on the seat.

In addition, the use of holes of circular cross-section, usually two toten in number, presents the advantage of reduced head loss, the circularcross-section being that presents the greatest hydraulic radius at givencross-sectional area.

The holes can be in a plane orthogonal to the axis of the needle.Nevertheless, it is possible for them to slope from upstream todownstream. This possibility gives a degree of freedom in addition tothose concerning the number and the diameter of the holes. A singleturned blank can thus be adapted to different injectors.

The above characteristics and others will appear better on reading thefollowing description of particular embodiments, given as non-limitingexamples. The description refers to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall view of an injector to which the invention isapplied;

FIG. 2 is an elevation view in half-section of the one-piece element ofthe injector shown in FIG. 1

FIG. 3 is a plan view of the guide of FIG. 2;

FIGS. 4 and 5 are section views on lines IV—IV and V—V of FIG. 3; and

FIG. 6 is a section view on lines VI—VI of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The injector whose general structure is shown in FIG. 1 comprises a body10 made up of a plurality of assembled-together parts, within whichthere is to be found a needle 12 that is movable axially by a coil 14.For this purpose, the needle is fixed to a ring 16 of ferromagneticmaterial. The needle could equally well be controlled electrically byother means, e.g. by a stack of piezoelectric pellets, or it could evenbe controlled by fluid pressure.

In the end portion 18 of the body 10 there is provided a bore 20 forguiding swellings 22 on the needle 12. The bore 20 connects via ashoulder 24 to a chamber 26 having a one-piece element 28 fixed thereto.In the case shown in FIG. 1, the element 28 is fixed by a circular weld32 made by laser or electron beam.

The element 28 constitutes a guide for the needle. To this end, it ispierced by a hole 42 of diameter such that the needle 12 can slidetherein as a sliding fit. This hole opens out above a bearing surfacefor the needle and surrounding the inlet to a spray orifice 30.

In the example shown, the shutter element of the injector is constitutedby the end of the needle 12. The bearing surface against which theneedle bears is conical in shape, for example, whereas the end of theneedle in its bearing zone is in the form of a spherical segment. Thetip of the end portion of the needle can be conical so as to reduce therisk of cavitation.

A spring 34 compressed between the rear face of the needle 12 and anendpiece 36, and whose position is adjustable for adjustment purposes,urges the needle 12 against the bearing surface. The coil 14 allows theneedle to be moved against the action of the spring 34 within limitsdetermined by the ring 16 coming into abutment against a fixed sleeve38, which can be made of a ferromagnetic material in order to completethe magnetic control circuit.

The one-piece element 28 is generally made of steel and manufactured byturning, machining its internal passages, polishing (e.g.electrochemically), and applying treatment to its surface or to itscore. Given that it is a single piece, it is possible to obtain highprecision concerning the relative locations of its various surfaces.

The element 28 is generally in the shape of a dual-cone. Between itsupstream and downstream terminal portions, of diameter suitable forenabling the elements to be engaged as a sliding fit in the chamber 26,there is provided a groove 40 (FIG. 2). A plurality of sloping feednotches 44 are cut through its upstream portion, there being four suchnotches in the example shown, each of which opens out into the groove40. A frustoconical chamfer can be provided between the upstream planeface of the element 28 and its cylindrical portion for greaterprogressivity.

The groove 40 communicates with the hole 42 via circular section bores46 that are also distributed angularly, there being two of them in theexample shown. These bores are oriented so as to open out tangentiallyinto the hole 42, in the annular gap between the line where the needlebears against its bearing surface and the cylindrical portion of theneedle, and that remains empty when the needle is pressed against thebearing surface. In practice, the bores open out in general immediatelyabove the bearing surface (FIGS. 4 and 5).

The presence of the groove 40 reduces the length of the bores 46, butthey must nevertheless retain sufficient length to set the fuel intorotation upstream from the bearing surface. In order to avoid giving thebores excessive length, the ratio of the diameter of the groove 40 tothe diameter of the hole 42 is generally about 2:1. In practice, thebores will generally be given a length that is greater than theirdiameter. The dead volume between the outlets of the bores and the seatis very small, so little fuel is sprayed crudely without any vortexeffect.

It can be seen that the path via which the fuel arrives upstream fromthe needle bearing surface comprises in succession:

annular clearance between the needle 12 and the inside wall of the endportion 18;

the notches 44 and the groove 40; and

the two to ten bores 46.

The above-described disposition presents numerous advantages. Fuel isdelivered in perfectly symmetrical manner because the element 28 iscentered in the chamber 26. The flow rate characteristics of theinjector can be modified in very simple manner, merely by providing aplurality of different sets of bores 46 and/or diameters for the sprayorifice 30. The annular clearance has no significant effect on the flowrate that the injector can deliver.

Instead of being placed in a plane that is orthogonal to the axis, thebores can slope downwards by as much as 45°, thereby providing anadditional parameter that can be adjusted.

What is claimed is:
 1. A fuel injector for injecting fuel into acombustion chamber of a spark ignition engine, comprising: an injectorbody having an axial passage, a one-piece element fixed within the bodyin a downstream portion of said axial passage, formed with a seatlocated between a spraying orifice and an axial bore, a needleterminated by a closure element for co-operating with said seat, saidneedle being slidably received in said bore and axially displaceablebetween a first axial position, in which the closure element bearsagainst the seat, and a second axial position in which the closureelement is spaced apart from the seat, said one-piece element beingdiabolo-shaped and co-operating with said downstream portion of the bodyto define an annular fuel feed chamber having a plurality of portscommunicating the fuel feed chamber with said bore immediately upstreamfrom the seat and opening out tangentially into the bore, and passagemeans for feeding the chamber with fuel from said axial passage.
 2. Aninjector according to claim 1, wherein the ports are cylindrical andhave a length greater than their transversal size.
 3. An injectoraccording to claim 1, wherein the ratio of an inside diameter of thechamber to a diameter of said bore is about 2:1.
 4. An injectoraccording to claim 1, having from two to ten said ports.
 5. An injectoraccording to claim 1, wherein said ports are located in a same planewhich is orthogonal to an axis of the needle.
 6. An injector accordingto claim 1 wherein the ports have a downward slope at an angle notexceeding 45°.
 7. An injector for injecting fuel into a combustionchamber of a spark ignition engine, comprising: an injector body, aone-piece element fixed within the body in a downstream portion thereof,formed with a seat communicating with a downstream spraying orifice andwith an upstream axial bore, a needle terminated by a closure elementco-operating with said seat, said needle being slidably received in saidbore and axially displaceable between a first axial position, in whichthe closure element closes the seat, and a second position in which theclosure element is spaced apart from the seat, said one-piece elementbeing diabolo-shaped and having an annular outer recess co-operatingwith said downstream portion of the body to define a fuel feed chamberhaving a plurality of ports communicating the chamber with said boreimmediately upstream from the seat and opening out tangentially into thebore, and passage means for feeding the chamber with fuel, comprising aplurality of sloping feed notches cut out in an upstream portion of theone-piece element, regularly distributed angularly, and opening out intothe recess of the one-piece element that defines the feed chamber.
 8. Aninjector according to claim 7, having a frustoconical chamfer between anupstream planar face of the one-piece element and a cylindrical portionthereof.
 9. A fuel injector for injecting fuel into a combustion chamberof a spark ignition engine, comprising: an injector body having a fuelinlet and an axial fuel flow passage, a one-piece element fixed withinthe body in a counterbore formed in a downstream portion of said passagein abutment against an end shoulder of said counterbore, formed with aseat communication with a fuel spraying orifice and with an axial bore,a needle terminated by a closure element for co-operating with saidseat, said needle being slidably received in said bore and axiallydisplaceable between a first axial position, in which the closureelement bears against the seat, and a second axial position in which theclosure element is spaced apart from the seat, said one-piece elementbeing diabolo-shaped and co-operating with said downstream portion ofthe body to define an annular fuel feed chamber having two to ten portscommunicating the chamber with said bore immediately upstream from theseat and opening out tangentially into the bore, and passage meanswithin said injector body and one-piece element for feeding the chamberwith fuel from said inlet.